The overall objective of the project is to determine whether weaning to a casein hydrolysate (Nutramigen TM) during at least the first 6 months of life reduces the incidence of Type 1 diabetes in genetically susceptible children. Specific Aims I-a: To determine, if weaning to casein hydrolysate reduces the frequency of diabetes-predictive autoantibodies in subjects with risk-associated HLA genotype and a first degree relative with type 1 diabetes. I-b: To determine, if weaning to casein hydrolysate reduces the frequency of clinical diabetes in subjects with risk-associated HLA genotype and an affected first degree relative. Newborn infants, who have increased genetic risk and first degree relatives with type 1 diabetes (mother, father or sibling has the disease, and HLA genotyping shows the subject to belong to the increased risk group) will be invited for the study. An international, multicenter, double blind, randomized, controlled trial of 2 different nutritional supplements will be performed. The newborn infants will be randomly allocated to receive after breast feeding 1 of 2 formulas during at least the first 6 months of life (the intervention period). The test formula will be a casein hydrolysate, free of intact cows milk proteins. The casein hydrolysate is not diabetogenic in the NOD mouse. The control formula will be similar to a commonly used cow milk based infant formula. Subjects will be followed during and after the intervention period for 6 and 10 years time during which serological markers are measured and the development of diabetes will be recorded. Such a clinical trial is necessary to get a definite answer to the hypothesis. Recruitment is carried out during a 2-year period in the U.S., Canada and 15 other countries. The estimated number of subjects participating in the randomized nutritional prevention study is approximately 2,800. This requires that genetic screening would be performed in approximately 6,200 newborn infants. The study question has important public health implications.